1. Technical Field
The present invention relates to a scooter-type motorcycle intake device in which an air cleaner box is provided on each side of a rear wheel.
2. Background Art
Conventionally, in a scooter-type motorcycle (hereinafter, referred simply to as scooter), a unit-swinging power train unit having an engine and a rear wheel is attached to a vehicle body frame in such a manner as to swing vertically. In a longitudinal direction of the scooter, a front end part of the power train unit is constituted by an engine, and a rear wheel supporting transmission case is attached integrally to a crankcase of the engine. A front end part of the engine is supported on the vehicle body frame in such a manner as to swing, and a rear end part of the transmission case is connected to the vehicle body frame via a cushion unit.
The transmission case is constructed so as to extend longitudinally on a left-hand side of the rear wheel, and power transmission devices for transmitting the drive of the engine to the rear wheel such as a V-belt type automatic transmission and a centrifugal clutch are incorporated therein.
An intake device that is provided on this type of power train unit adopts a construction in which intake air is induced from an air cleaner box provided above the transmission case into a cylinder through a carburetor above the crankcase.
The interior of the air cleaner box is partitioned into an upstream-side air compartment and a downstream-side air compartment by an air cleaner element, and a fresh air inlet is opened in the upstream-side air compartment, whereas the carburetor is connected to the downstream-side air compartment via an intake duct.
Incidentally, in the conventional intake device that has been described above, since the capacity of the air cleaner box is small, there has existed a limitation on the attempt to increase the output of the engine by increasing the displacement thereof. Namely, this is because, when attempting to increase the amount of intake air by increasing the displacement of the engine, the flow of intake air in the air cleaner box gets faster, and this leads to an excessive increase in intake resistance.
While a drawback like this can be resolved by increasing the capacity of the air cleaner box, in the event that this resolution is adopted, the external shape of the air cleaner box is enlarged, whereby there is caused instead a problem that the vehicle body is made larger in size in association with the enlargement of the external shape of the air cleaner box.